This invention relates to an infrared rays detecting apparatus having a tube on which an infrared rays sensor of the multi-element type is carried.
Infrared rays sensors are employed in many fields, for example, for meteorological observation by means of an artificial satellite, prevention of crimes, accident prevention, geological and/or resource survey, and medical treatment by infrared rays thermography since they can detect presence, shapes, temperatures, compositions and so forth of target bodies without contacting with the bodies. Among such infrared rays sensors, sensors of the photoelectric conversion type which employ a binary or ternary compound semiconductor are high in sensitivity and also in responding speed, but it is normally necessary to cool an element substantially to the temperature of liquid nitrogen.
To this end, an infrared rays detecting apparatus which incorporates therein such an infrared rays sensor as described above normally has the following construction. In particular, an infrared rays transmitting window is provided at a portion of a vacuum insulated vessel of the dual structure including an inner tube and an outer tube, and an infrared rays sensor composed of a plurality of elements is disposed at a top portion of the inner tube in an opposing relationship to the infrared rays transmitting window. Either such coolant as liquid nitrogen is contained in the inner tube of the insulated vessel or a low temperature cooling apparatus of the Joule-Thomson type or the like is installed to cool the infrared rays sensor substantially to the temperature of liquid nitrogen during operation of the infrared rays sensor.
In order to extract a signal from such infrared rays sensor, the following construction is employed. In particular, gold is vapor deposited on a surface of the inner tube to which the infrared rays sensor is adhered to form a deposited gold film, and the deposited gold film is cut to form a grounding line and element lines, which are individually connected by way of bonding wires to a common ground electrode terminal and a plurality of output electrodes of the infrared rays sensor. Further, the element lines and grounding line are connected by way of bonding wires to a plurality of gold patterns formed on an annular ceramic substrate disposed around the inner tube so as to extract signals from the gold patterns.
In such an infrared rays detecting apparatus as described above, a loop is formed by an element line and the grounding line formed on the inner tube. However, where the loop has a comparatively great area, if, for example, the infrared rays detecting apparatus is vibrated or an external magnetic field is fluctuated, an electromotive force produced in the loop will make a noise source and correct signals cannot be extracted from the infrared rays detecting apparatus. Accordingly, an infrared rays detecting apparatus is demanded which minimizes production of noises and allows extraction of correct signals.
FIG. 1 is a schematic view showing construction of an exemplary one of conventional infrared rays detecting apparatus. Referring to FIG. 1, reference numeral 10 denotes a vacuum insulated vessel which is carried on a helium circulating cooler 12. The vacuum insulated vessel 10 includes an outer tube 14 made of Kovar and an inner tube 16 made of glass. The outer and inner tubes 14 and 16 are both mounted on a mounting member 18 made of Kovar, and the mounting member 18 is secured to a support member 20 mounted on the helium circulating cooler 12. Reference numeral 22 denotes an annular ceramic substrate for extracting leads from the vacuum insulated vessel 10 to the outside, and the annular ceramic substrate 22 is mounted in a sandwiched condition on the outer tube 14. Meanwhile, an infrared rays sensor 24 of the multi-element type made of HgCdTe or the like is adhered to an upper end face of the inner tube 16. Further, a germanium window 14a for introducing infrared rays therethrough is provided at a top portion of the outer tube 14.
Referring now to FIG. 2, there is shown a partly omitted perspective view of the infrared rays detecting apparatus of FIG. 1 but with the outer tube 14 removed, and particularly a wiring condition from the infrared rays sensor 24 to conductive patterns on the annular ceramic substrate 22 can be seen clearly. As shown in FIG. 2, a grounding line E and first to twelfth element lines L1 to L12 are formed on an upper end face and a side face of the inner tube 16, and a common grounding electrode and a plurality of output electrodes of the infrared rays sensor 24 are connected by bonding gold wires 25 to the grounding line E and element lines L1 to L12. The grounding line E and element lines L1 to L12 are formed by vapor depositing gold to a surface of the inner tube 16 to form a deposited gold film and cutting the deposited gold film with a laser beam, etching or the like to separate them in a predetermined spaced relationship from each other. Meanwhile, a number of metal patterns 22a corresponding to the number of the grounding line E and element lines L1 to L12 are vapor deposited on the annular ceramic substrate 22, and the gold patterns 22a and the grounding line E and element lines L1 to L12 are individually connected to each other by bonding gold wires 27.
With the construction described above, when the helium circulating cooler 12 operates, the infrared rays sensor 24 is cooled substantially to the temperature of liquid nitrogen by way of a rod 26 made of stainless steel and a heat conducting spring 28 made of a copper alloy to detect infrared rays.
By the way, on the inner tube 16 of the conventional infrared rays detecting apparatus shown in FIG. 2, loops are formed by the element lines L1 to L12 and the grounding line E. Where a loop is formed, for example, by the sixth element line L6 and the grounding line E, such a loop R as shown in FIG. 3 is formed.
In a condition wherein the loop R is formed in this manner, if, for example, the infrared rays detecting apparatus is vibrated or an external magnetic field is fluctuated, such an electromotive force V as defined by an expression (1) given below is produced in the loop R. Since the electromotive force V increases in proportion to a loop area S as can be seen from the expression (1), where the loop area is great, the electromotive force V is high accordingly, which will make a noise source. Accordingly, it is a problem that correct detection cannot be accomplished. EQU V=-B(dS/dt) (1)
In the expression (1), B is a magnetic flux density [wb/m.sup.2 ], and S is a loop area [m.sup.2 ]of the loop R.